motorcycle tires

Abstract

The motorcycle tire provided by the present invention can maintain the wear resistance when driving straight and improve the grip performance when turning. A motorcycle tire includes a tread portion (2). The tread portion (2) includes: a base rubber layer (10) and a top rubber layer (11) arranged on the radially outer side of the base rubber layer (10) and constituting the contact surface of the tread portion (2). The top rubber layer (11) includes: a crown top (12) arranged at the central part of the tire axial direction, and a pair of shoulder tops (13) arranged on both sides of the crown top (12) in the tire axial direction. The loss tangent of the crown top 12 at 0°C, i.e., tanδc, the loss tangent of the shoulder top (13) at 0°C, i.e., tanδs, and the loss tangent of the base rubber layer (10) at 0°C, i.e., tanδb, satisfy the following formula (1): tanδc<tanδs≤tanδb.

Description

Technical Field

[0001] The present invention relates to a tire for motorcycles. Background Art

[0002] Various motorcycle tires with improved tread rubber have been proposed. For example, Patent Document 1 below proposes a pneumatic motorcycle tire that achieves excellent durability and handling stability by using a rubber composition containing a larger amount of oil in the shoulder rubber layer of the tread rubber than in the base rubber layer.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2018-76002

[0004] In recent years, with the improvement of the performance of motorcycles, there is a need for motorcycle tires with excellent gripping performance when turning. However, in motorcycle tires, if the gripping performance is improved, the wear resistance during straight driving will be damaged. Summary of the Invention

[0005] The present invention has been made in view of the above-mentioned actual situation, and its main object is to provide a motorcycle tire that maintains wear resistance during straight running and improves grip performance during cornering.

[0006] The motorcycle tire of the present invention includes a tread portion, wherein the tread portion includes: a base rubber layer, and a top rubber layer arranged on the radially outer side of the base rubber layer and constituting the ground contact surface of the tread portion, the top rubber layer includes: a crown top arranged in the axial center of the tire, and a pair of shoulder tops arranged on both sides of the crown top in the axial direction of the tire, the loss tangent of the crown top at 0°C, i.e., tanδc, the loss tangent of the shoulder top at 0°C, i.e., tanδs, and the loss tangent of the base rubber layer at 0°C, i.e., tanδb, satisfy the following formula (1).

[0007] tanδc<tanδs≤tanδb…(1)

[0008] In the motorcycle tire of the present invention, it is preferable that the base rubber layer at the inner side in the tire radial direction of the shoulder top is thicker than the base rubber layer at the inner side in the tire radial direction of the crown top.

[0009] In the motorcycle tire of the present invention, it is preferable that the thickness of the base rubber layer continuously increases from the center portion in the tire axial direction toward both outer sides in the tire axial direction.

[0010] In the motorcycle tire of the present invention, it is preferable that the JIS-A hardness of the shoulder top is in a range of -2 degrees to +5 degrees relative to the JIS-A hardness of the crown top.

[0011] In the motorcycle tire of the present invention, preferably, the maximum axial width of the ground contact surface of the crown is 20% to 60% of the maximum axial width of the ground contact surface of the tread portion.

[0012] In the motorcycle tire of the present invention, preferably, the base rubber layer has a thickness in the tire radial direction inner side of the crown top that is 10% to 40% of the total thickness of the tread rubber constituting the tread portion.

[0013] In the motorcycle tire of the present invention, it is preferred that a plurality of grooves be provided on the ground contact surface of the tread portion, and the depth of each of the plurality of grooves be smaller than the thickness of the top rubber layer.

[0014] The motorcycle tire of the present invention, by adopting the above-mentioned structure, can maintain the wear resistance during straight running and improve the grip performance during cornering. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a cross-sectional view showing one embodiment of the motorcycle tire of the present invention.

[0016] Figure 2 yes Figure 1 An enlarged view of the tread.

[0017] Explanation of Reference Numerals: 2 ... tread portion; 10 ... base rubber layer; 11 ... top rubber layer; 12 ... crown top; 13 ... shoulder top. DETAILED DESCRIPTION

[0018] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

[0019] Figure 1 This is a cross-sectional view of a motorcycle tire 1 (hereinafter sometimes referred to as "tire") according to this embodiment, taken along a tire meridian including the tire's rotation axis, in its normal state. The tire 1 of this embodiment is suitable for use on the rear wheel of a motorcycle used for road sports. However, the tire of the present invention is not limited to this embodiment.

[0020] For pneumatic tires with specified specifications, the "normal condition" refers to the condition in which the tire is assembled on a standard rim, inflated to the specified internal pressure, and unloaded. For tires with unspecified specifications, the normal condition refers to the standard operating condition corresponding to the tire's intended use and means an unloaded condition. Unless otherwise specified in this specification, dimensions of various tire components are values ​​measured under this normal condition.

[0021] "Regular rims" are rims that have specifications specified for each tire within the standard system that includes the tire's specifications. For example, JATMA has "standard rims," ​​TRA has "design rims," ​​and ETRTO has "measuring rims."

[0022] "Normal internal pressure" is the air pressure specified for each tire in the specification system that includes the specifications to which the tire is based. If it is JATMA, it is the "maximum air pressure". If it is TRA, it is the maximum value recorded in the table "TIRE LOAD LIMITS ATVARIOUS COLD INFLATION PRESSURES". If it is ETRTO, it is "INFLATION PRESSURE".

[0023] like Figure 1 As shown, the tire 1 of this embodiment includes a tread portion 2, a pair of sidewall portions 3, and a pair of bead portions 4. The sidewall portions 3 are connected to both sides of the tread portion 2 in the tire axial direction. The bead portions 4 are connected to the radially inner side of the sidewall portions 3. The tread portion 2 has a contact surface between one tread end Te and the other tread end Te that is convex toward the tire radial outer side and is curved in an arc shape so as to ensure a sufficient contact area even when turning at a large camber angle.

[0024] The tire 1 of the present embodiment includes a carcass 6 extending from one bead portion 4 through one sidewall portion 3 , the tread portion 2 , and the other sidewall portion 3 to the other bead portion 4 .

[0025] The carcass 6, for example, includes a carcass ply 6A comprising a plurality of carcass cords. The carcass 6 in this embodiment is, for example, composed of two carcass ply 6A. The carcass ply 6A includes a main body portion 6a and a turnback portion 6b. The main body portion 6a extends from the tread portion 2 through the sidewall portions 3 on both sides to the bead cores 5 of the bead portions 4 on both sides. The turnback portion 6b is connected to the main body portion 6a and folds around the bead core 5 from the inner side to the outer side in the tire's axial direction.

[0026] The tread portion 2 is provided with, for example, a belt layer 7. The belt layer 7 comprises, for example, a belt ply comprising a plurality of belt cords inclined at 10 to 45 degrees relative to the tire circumferential direction. While the belt layer 7 in this embodiment consists of a single belt ply, multiple belt plies may be stacked. Such a belt layer 7 effectively reinforces the tread portion 2.

[0027] Figure 2 An enlarged view of the tread portion 2 is shown in FIG. Figure 2As shown, the tread portion 2 includes a carcass 6 and a tread rubber 2G disposed radially outward of the belt layer 7. The tread rubber 2G of the tread portion 2 includes a base rubber layer 10 and a top rubber layer 11 disposed radially outward of the base rubber layer 10 and constituting the ground contact surface of the tread portion 2.

[0028] The top rubber layer 11 includes a crown top portion 12 disposed in the center portion of the tire in the axial direction, and a pair of shoulder top portions 13 disposed on both sides of the crown top portion 12 in the tire axial direction.

[0029] In the present invention, the loss tangent at 0°C of the crown top 12, tan δc, the loss tangent at 0°C of the shoulder top 13, and tan δb of the base rubber layer 10 satisfy the following formula (1).

[0030] tanδc<tanδs≤tanδb…(1)

[0031] In this specification, the "loss tangent tan δ" is a value measured using a "viscoelastometer" manufactured by Iwamoto Seisakusho Co., Ltd. under the following conditions in accordance with the provisions of JIS-K6394.

[0032] Initial deformation: 10%

[0033] Amplitude: ±1%

[0034] Frequency: 10Hz

[0035] Deformation Mode: Stretch

[0036] Measurement temperature: 0℃

[0037] In the present invention, by adopting the above-mentioned structure, it is possible to maintain the wear resistance during straight running while improving the grip performance during cornering. The reason for this is presumably the following mechanism.

[0038] In the present invention, the loss tangent tanδs at the shoulder top 13 is greater than the loss tangent tanδc at the crown top 12. Therefore, the crown top 12, which contacts the ground during straight driving, generates relatively low heat, maintaining its wear resistance. Meanwhile, the shoulder top 13, which contacts the ground during cornering, generates moderate heat due to deformation of the tread rubber 2G, enabling excellent grip performance during cornering.

[0039] Furthermore, in the present invention, the loss tangent tanδb of the base rubber layer 10 is greater than the loss tangent tanδs of the shoulder top 13, so higher heat generation can be expected in the base rubber layer 10. Consequently, during straight driving with the crown top 12 in contact, or during cornering at a relatively small camber angle, the deformation of the tread rubber 2G is relatively small, resulting in less heat generation in the base rubber layer 10, thereby maintaining wear resistance during straight driving. Furthermore, during cornering with the shoulder top 13 in contact, the deformation of the tread rubber 2G is large, resulting in moderate heat generation in the base rubber layer 10, further improving grip at the shoulder top 13. In the present invention, it is believed that this mechanism maintains wear resistance during straight driving while improving grip during cornering.

[0040] The following describes the structure of this embodiment in further detail. Furthermore, each of the structures described below represents a specific embodiment of this embodiment. Therefore, it goes without saying that the present invention can achieve the aforementioned effects even without the structures described below. Furthermore, in the tire of the present invention having the aforementioned features, even if any one of the structures described below is applied individually, improved performance corresponding to each structure can be expected. Furthermore, when several of the structures described below are applied in combination, improved performance corresponding to the combined structure can be expected.

[0041] In this embodiment, the above-mentioned loss tangent tanδc of the crown top 12 (hereinafter sometimes referred to as "tanδc", the above-mentioned loss tangent tanδs of the shoulder top 13 (hereinafter sometimes referred to as "tanδs"), and the above-mentioned loss tangent tanδb of the base rubber layer 10 (hereinafter sometimes referred to as "tanδb") are respectively formed to be, for example, 0.20 to 1.60. More specifically, tanδc is, for example, 0.20 to 0.90, preferably 0.70 to 0.90. tanδs is, for example, 0.80 to 1.40, preferably 0.90 to 1.10. tanδb is, for example, 0.80 to 1.60, preferably 1.00 to 1.20.

[0042] Furthermore, tanδs is, for example, 105% to 140% of tanδc, preferably 105% to 120%. tanδb is preferably greater than tanδs. tanδb is more preferably 100% to 140% of tanδs, and even more preferably 105% to 120%. This allows for the aforementioned effects to be achieved while also preventing damage such as peeling of the rubber layers.

[0043] The JIS-A hardness of the shoulder top 13 is preferably within a range of -2 to +5 degrees relative to the JIS-A hardness of the crown top 12. This can achieve the aforementioned effects, improve the transient response characteristics when the vehicle body is tilted, and suppress uneven wear at the boundary between the crown top 12 and the shoulder top 13.

[0044] In this specification, JIS-A hardness means the hardness of rubber at 25° C. measured by a type A durometer based on JIS-K6253.

[0045] Likewise, the JIS-A hardness of the base rubber layer 10 is preferably in the range of -2 to +5 degrees relative to the JIS-A hardness of the shoulder top 13. This can suppress separation between the base rubber layer 10 and the shoulder top 13 during cornering.

[0046] The rubber layer having the above-mentioned characteristics can be obtained by appropriately combining known materials used in rubber production.

[0047] The thickness of the base rubber layer 10 on the inner side of the tire radial direction at the shoulder top 13 is preferably greater than the thickness of the base rubber layer 10 on the inner side of the tire radial direction at the crown top 12. Such a base rubber layer 10 can maintain wear resistance during straight running while reliably improving grip performance during cornering.

[0048] In a further preferred embodiment, the thickness of the base rubber layer 10 increases continuously from the center portion in the tire axial direction toward both outer sides in the tire axial direction. This can improve the transient response characteristics when the vehicle body rolls over.

[0049] The thickness t2 of the base rubber layer 10 at the center of the contact patch at the shoulder top 13 (the center of the contact patch in the longitudinal direction of the tire cross section) is preferably 1.5 times or more, more preferably 1.8 times or more, and preferably 2.5 times or less, more preferably 2.2 times or less of the thickness t1 of the base rubber layer 10 at the tire equator C. This improves both wear resistance during straight running and grip performance during cornering in a balanced manner.

[0050] The thickness of the base rubber layer 10 on the tire radially inner side of the crown 12 is preferably at least 10% of the total thickness of the tread rubber 2G constituting the tread portion 2 (the thickness from the ground contact surface to the outer surface of the belt layer), and more preferably 10% to 40%. Furthermore, the minimum thickness of the base rubber layer 10 on the tire radially inner side of the crown 12 (in this embodiment, thickness t2 at the tire equator C) is 10% to 20% of the total thickness of the tread rubber 2G. This ensures that the wear resistance of the crown 12 is reliably maintained.

[0051] The maximum axial width W2 of the contact patch of the crown top 12 is equal to the maximum axial width W1 of the contact patch of the tread portion 2 ( Figure 1 As shown in FIG, the wear resistance of the tire is maintained at 20% to 60% of the tire, preferably 20% to 40%.

[0052] The tread rubber 2G of this embodiment is composed only of the above-mentioned base rubber layer 10 and top rubber layer 11, without any other rubber components. This ensures the above-mentioned effects. However, the present invention is not limited to this embodiment.

[0053] The contact surface of the tread portion 2 may also be provided with a plurality of grooves 15. In this case, the depth of each of the plurality of grooves 15 is preferably less than the thickness of the top rubber layer 11. In other words, the base rubber layer 10 is preferably not exposed on the inner surface of the grooves 15. This prevents the base rubber layer from being exposed even as the tread portion 2 wears, ensuring continued excellent wear resistance and handling stability.

[0054] As mentioned above, the motorcycle tire according to one embodiment of the present invention has been described in detail. However, the present invention is not limited to the above-mentioned specific embodiment, but can be implemented in various modified forms.

[0055] [Example]

[0056] Based on the specifications in Table 1 and Table 2, Figure 1 A motorcycle tire (rear wheel tire) with a basic structure of 180 / 55R17 was produced. A tire with a crown rubber composed of a single rubber was also produced as a comparative example. The comparative example tire had substantially the same structure as the tire in the example, except for the above-mentioned items. Each test tire was tested for wear resistance during straight driving, grip performance during straight driving, grip performance during cornering, and handling stability. The common specifications and testing methods for each test tire are shown below.

[0057] - Rim size: MT5.50

[0058] Tire internal pressure: 250kPa

[0059] Test vehicle: Displacement 1000cc

[0060] Wear resistance during straight driving

[0061] The remaining rubber thickness in the center of the tread was measured after the test tires were driven on ordinary roads for 10,000 km. The results were indexed, with the rubber thickness of the comparative example being 100. A larger value indicates greater rubber thickness and better wear resistance.

[0062] <Straight-driving grip, cornering grip, and handling stability>

[0063] The driver evaluated the grip performance of the tires during straight driving, grip performance during cornering, and handling stability while driving on a circular course. The results were scored with the comparative example as 100, with larger values ​​indicating better performance.

[0064] The test results are shown in Tables 1 and 2.

[0065]

Table 1

[0066]

[0067]

Table 2

[0068]

[0069] The test results confirmed that the tires of the examples maintained their wear resistance during straight driving while improving their grip performance during cornering. Furthermore, it was confirmed that the tires of the examples exhibited excellent steering stability.

Claims

1. A motorcycle tire comprising a tread portion, characterized in that: The tread portion includes a base rubber layer and a top rubber layer disposed on the outer side of the base rubber layer in the tire radial direction and constituting a ground contact surface of the tread portion. The top rubber layer includes a crown top portion disposed in the center of the tire in the axial direction, and a pair of shoulder top portions disposed on both sides of the crown top portion in the axial direction of the tire. The loss tangent of the crown at 0°C, i.e., tan δc, the loss tangent of the shoulder at 0°C, i.e., tan δs, and the loss tangent of the base rubber layer at 0°C, i.e., tan δb, satisfy the following formula (1): The tanδc is 0.70 to 0.90, The tanδs is 0.90 to 1.10, tanδc<tanδs≤tanδb…(1).

2. The motorcycle tire according to claim 1, wherein: The thickness of the base rubber layer at the inner side of the shoulder top in the tire radial direction is greater than the thickness of the base rubber layer at the inner side of the crown top in the tire radial direction.

3. The motorcycle tire according to claim 1 or 2, wherein: The thickness of the base rubber layer continuously increases from the center portion in the tire axial direction toward both outer sides in the tire axial direction.

4. The motorcycle tire according to claim 1 or 2, characterized in that: The JIS-A hardness of the shoulder top is within a range of -2 degrees to +5 degrees relative to the JIS-A hardness of the crown top.

5. The motorcycle tire according to claim 1 or 2, characterized in that: The maximum axial width of the ground contact surface of the crown top is 20% to 60% of the maximum axial width of the ground contact surface of the tread portion.

6. The motorcycle tire according to claim 1 or 2, characterized in that: The base rubber layer has a thickness of 10% to 40% of the total thickness of the tread rubber constituting the tread portion at an inner side of the crown in the tire radial direction.

7. The motorcycle tire according to claim 1 or 2, wherein: A plurality of grooves are provided on the contact surface of the tread portion. The depth of each of the plurality of grooves is smaller than the thickness of the top rubber layer.

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